Considering that gyarados has intimidate NOT moxie so please dont bring that up

They both learn good attacking moves that provide near perfect coverage(Waterfall and bounce only resisted by lanturn and empoleon and rotomw)(Outrage and waterfall only resisted by empoleon and ferrothron)
Gyarados has much higher attack but kingdra has outrage which has much higher power than any of gyarados's moves which basically makes them have equal power
Kingdra has only 1 weakness while gyarados has 2 and one of them is a crippling electric weakness which is a quite popular attacking type in ou right now

Well, you have mentioned some good points, and I would say Kingdra. As you said, that Electric weakness is pretty bad as of late. Kingdra also works better on a Rain team IMO, due to Swift Swim. Sniper is also a nice option to have.
May I also add that Kingdra was blessed with even stats, making it quite possible for it to survive longer while setting up D-Dance. Gyarados just doesn't have any Defensive Bulk.Edit: Just remembered Intimidate on Gyarados. Thought I should mention that that Attack lowering ability does nothing against Discharge.

Just as a side note, Bounce isn't really a great move for competitive battling.

Kingdra in my opinion.It only has one weakness and has more coverage to me.Don't get me wrong.Gyarados has awesome attack power,but if you are not fast enough to clear electric types goodbye gyarados.So in my opinion kingdra is a much better choice.

well its kinda risky relying on crits with scope lens because the crit percentage increase is not that huge so i was thinking to use a substitute dragon dance version so i could avoid all statuses who try to stop my sweep. but thanks for advice, you guys made me consider kingdra over gyarados lol

Scope lens and focus energy is a waste of a item space and a turn
Id rather raise its attack using a life orb and atk+spd using dragon dance
That would almost double the atk, raise spd to 1.5,
instead of raing the crit to pathetic 25% chance